The Logistics of Electromagnetic Locks

Electromagnetic locks (EMLs) have become a popular mean to electrically control access to almost any door in just about any type of occupancy. In April of last year, Locksmith Ledger provided direction on various levels with regard to the installation of EMLs (see http://bit.ly/2DoltgQ). In today’s Locksmith Ledger article, we will chat about the history, legalities, and applications where these electrically-operated locks are commonly applied.

Historically, the first modern EML was engineered by Sumner Saphirstein in 1969, as a means of locking doors at the Montreal Forum while complying with fire protection concerns by local authorities. That concern then, just as now, relates to the automatic closure of all EML-equipped doors if a fire should occur.

“Saphirstein initially proposed to use a linear stack of door holders to work as an electromagnetic lock. These door holders were traditionally used to hold doors open, but in this application Saphirstein believed that they could be packaged and adapted to work as a fail-safe lock,” (Source: Wikipedia, http://bit.ly/2sDAaqd, see photo).

Saphirstein’s invention worked while observing the concerns of local fire authorities. He continued to work on the basic design principle until he achieved an early version of today’s EML. It was Saphirstein’s efforts to create an effective locking device that resulted in the establishment of the Locknetics company. Here, accessories and control circuits for the EML were further developed. Today, Locknetics is an Allegion brand and a major player in nursing homes, hospitals, and other applications where advanced ingress and egress features are employed (See the list of EML manufacturers at the end of this story for additional sources).

Legalities Behind EML Usage

When we say ‘legality,’ it’s in reference to authoritative requirements associated with any and all types of fire alarm systems and attached components. This includes all EMLs no matter where they are installed. The way this works is that a national fire code-making organization, like the National Fire Protection Association (NFPA) of Quincy, MA, creates code documents which contain specific requirements in reference to any and all technological issues involving fire detection, life-safety functions, and other aspects of fire protection. Those requirements then are institutionalized by each State as well as the various municipalities therein and thus enforced by legal means by local fire inspectors, State fire protection officers, fire marshals, and others, some whom have arrest powers at their disposal.

For example, NFPA 101, entitled ‘Life Safety Code,’ defines ‘where,’ ‘when,’ and the ‘circumstances’ by which an EML is to be used. This fire code document explains what you’re supposed to do in a variety of environments, which is called an ‘occupancy.’

“The state of New Hampshire has adopted NFPA 101. As a career firefighter I have the ability to look up codes and get quick answers from AHJ’s. When in doubt, contact the AHJ, in my case normally the fire chief of the town/city. You disclose what system you would like to install in writing and he’ll physically sign off on it, especially for the more specialty installs,” says Brian Akerley, a project manager with A & B Lock and Security of Gilford, NH.

A good case in point is Section 7.2.1.8.1 contained in NFPA 101. It states, “A door leaf normally required to be kept closed shall not be secured in the opened position at any time and shall be self-closing or automatic-closing in accordance with 7.2.1.8.2, unless otherwise permitted by 7.2.1.8.3.” This passage touches on the very issue of electric door closer openers, door holder closers, and electrified door holders.

Within Section 7.2.1.8.2, there’s a long list of methods whereby this type of door--which is usually a fire door--can be held open. One method cited is that of a ‘hold-open mechanism,’ also referred to as a ‘door holder, as referenced in Wikipedia’s Saphirstein quote in the first section above (see photo).

And then there’s NFPA 72, entitled ‘National Fire Alarm and Signaling Code.’

“NFPA 72, for example, tells us how the EML must operate in conjunction with a fire alarm [control] panel,” says Akerley. “First, the power supply must be properly connected to a fire alarm relay device that’s properly rated and listed. Second, there must be a [properly listed] motion detector [releasing device] to provide automatic egress. And third, there must be a REX (Request to Exit) switch on the wall [next to the door] that connects directly to the EML.”

Section 21.8.4 of NFPA 72 also says that electrically-operated magnetic door holders do not require a Secondary Power Supply, which, in most cases, is a stack of batteries with a charging system to assure that they’re properly maintained.

When secondary power is required or needed, Section 21.9.2 says that you must follow Section 10.6.7, which provides direction on a variety of matters. One example is battery capacity, which must include an additional 20 percent over calculations for headroom. Also, it’s required that these EM door holders and/or EMLs not interfere with the proper function of the fire detection/protection system itself, etc.

Where EMLs are Sanctioned for Use

In order to better understand where EMLs are commonly used it helps to understand why they are needed. There must be a balance between life safety and security. Fire authorities, such as local fire inspectors, building code enforcement, plan examiners, those that issue permits, and others, would like nothing more than to ignore security in lieu of life safety, but insurance companies, law enforcement, home and business owners, and other stakeholders won’t allow it. So a balance must be maintained between the two considerations and that’s what fire codes are for.

Security is an important aspect of everyday living that must be considered, not only from the standpoint of physical assets, but also the very lives of those who live, work, or do business within these facilities. With this in mind, an EML is acceptable in almost any situation where life safety and security hang in the balance.

The following is a short list of common applications where EMLs are used. It’s by no means complete, but it may stimulate some thought concerning possible applications that you’re faced with at this very moment in time within your own business:

Nursing homes
Hospitals
Schools
Tool rooms
Computer rooms
Multiple-tenant high rise buildings
Multiple-family housing complexes
Automated access for laundromats
Libraries
Government buildings

The list is virtually endless, but the commonality between them all is the fact that the EMLs you use must be tested and listed by a third-party testing organization, like United Laboratories (UL).

EML Technical Specifications and Considerations

There are essentially two basic types of EMLs available on the market today -- interior and exterior. All of them are ‘fail safe’ devices, which means that when power is taken away, or if they should fail to operate, the respective doors will reside in an unlocked condition, thus ensuring timely egress. The primary difference between them is holding power, usually measured in pounds. For example, in one product line, an external EML is rated with a holding force of 1200 pounds with a current draw of 250 mA at 12 VDC, or 150 mA at 24 VDC. For comparison, their inside version, rated at 600 pounds, has a current draw of 300 mA at 12 VDC; and 150 mA at 24 VDC.

There’s an advantage to using 24 VDC over that of 12 VDC. It concerns the adverse effect of higher currents which means the use of larger gauge wire, which, in turn, carries a higher cost than the lower voltage model.

The distance you can run an EML using lower voltages is also a factor to consider. A higher current specification at longer linear distances means an even larger gauge wire is needed--thus costing you even more money. Also, if you happen to miss calculate and run too small a cable, the voltage drop across it from power supply to EML(s) can require you to install an additional power supply at each door.